1. Field of the Invention
The present invention generally relates to gas laser angular rate sensors, also known and referred to in the art as Ring-Laser Gyros (RLGs), and more particularly to an improved system for energizing an RLG in order to extend its operating life.
2. Description of the Prior Art
An integral part of a ring-laser gyro is the laser beam source or generator. One type of laser beam generator comprises electrodes and a discharge cavity in combination with a plurality of mirrors which define a closed path. The path is usually triangular but other paths such as rectangular can be used.
Present day ring-laser gyros employ a gas discharge cavity filled with a gas which is excited by an electric current passing between the electrodes ionizing the gas and creating a plasma. As is well understood by those skilled in the art, the ionized gas produces a population inversion which results in the emission of photons, and in the case of He-Ne, a visible light is generated which is indicative of the plasma. If the gas discharge cavity is properly positioned with respect to the plurality of mirrors, the excited gas will result in two counterpropagating laser beams traveling in opposite directions along an optical, closed-loop path defined by the mirrors.
In some embodiments of ring laser gyros, a unitary body provides the gas discharge cavity including the optical closed-loop path. Such a system is shown in U.S. Pat. No. 3,390,606 by Podgorski, which is assigned to the same assignee as the present invention. There an optical cavity is formed in a unitary block. A selected lasing gas is used to fill the optical cavity. Mirrors are positioned around the optical cavity at appropriate locations such that counterpropagating beams are reflected so as to travel in opposite directions along the optical cavity. A gas discharge is created in the gas filled optical cavity by means of an electrical current flowing in the gas between at least one anode and at least one cathode which are both in communication with the gas filled optical cavity.
It should be noted that prior art ring-laser gyro systems often have a pair of anodes and a single cathode which produce two electrical currents flowing in opposite directions. Each of the electrical discharge currents create plasma in the gas. Each current is established by an applied electrical potential, of sufficient magnitude, between one cathode and one anode. Alternately, the RLG may have two cathodes and one anode.
Various factors both external and internal to the RLG can effect beam intensity. Temperature is one external factor. A change in a cavity parameter is example of an internal factor. In the prior art, RLGs are commonly operated with essentially a constant power or constant current input which results in a variable beam intensity due to external or internal factors. A certain magnitude of operating current is selected which under a specified range of external and internal conditions produces a beam whose intensity is adequate for satisfactory operation. However, it has been determined that the useful life of the cathode is a function of the magnitude, over time, of the current it must carry; the greater the magnitude the shorter the useful life of the cathode. In addition, the useful operating life of internal elements of the RLG, such as mirrors, is a function of the magnitude of the operating current; the higher the current, the shorter the operating life. These internal and external factors have caused RLGs to be operated with a higher current than necessary during part of their operating life in order to produce a beam intensity satisfactory for operation under all conditions, thus shortening the potential operational life of the RLG.